Orientation Controls
What are Orientation Controls?
Orientation controls define how a feature's angle or direction relates to a datum reference frame. Unlike form controls, orientation controls always reference at least one datum.There are three orientation controls:
| Symbol | Name | Controls |
|---|---|---|
| ∥ | Parallelism | Surface or axis parallel to datum |
| ⊥ | Perpendicularity | Surface or axis 90° to datum |
| ∠ | Angularity | Surface or axis at specified angle |
1. Parallelism (∥)
Definition: Controls how parallel a surface or axis must be to a datum.Surface Parallelism
The surface must lie between two parallel planes that are parallel to the datum:
FCF: ┌───┬──────┬────────┐
│ ∥ │ 0.1 │ A │
└───┴──────┴────────┘
Datum A ═══════════════════════
═══════════════ 0.1 tolerance zone
~~~~~~~~~~~~~~~~~~~~ (actual surface)
═══════════════Axis Parallelism
When applied to a feature of size, the axis must lie within a cylindrical zone parallel to the datum:
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FCF: ┌───┬────────┬────────┐
│ ∥ │ ⌀ 0.1 │ A │
└───┴────────┴────────┘2. Perpendicularity (⊥)
Definition: Controls how perpendicular (90°) a surface or axis must be to a datum.Surface Perpendicularity
The surface must lie between two parallel planes perpendicular to the datum:
FCF: ┌───┬──────┬────────┐
│ ⊥ │ 0.08 │ A │
└───┴──────┴────────┘
│ │ 0.08 zone
Datum A ════╪═╪════════════
│ │
│ │ (actual surface)Axis Perpendicularity
The axis must lie within a cylindrical zone perpendicular to the datum plane:
FCF: ┌───┬────────┬────────┐
│ ⊥ │ ⌀ 0.1 │ A │
└───┴────────┴────────┘3. Angularity (∠)
Definition: Controls a surface or axis at any angle other than 0° or 90° to a datum.FCF: ┌───┬──────┬────────┐
│ ∠ │ 0.1 │ A │
└───┴──────┴────────┘
Basic angle: 45°
╲
╲ 0.1 tolerance zone
Datum A ═══╲═════════════
╲ 45°Important: The basic angle (e.g., 45°) is shown separately on the drawing, not in the FCF. The FCF only shows the tolerance.Use Case: Chamfers, tapered features, angled mounting surfaces.
Orientation vs. Form
Orientation controls inherently control form as well:
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| Control | Controls Form? | Controls Orientation? |
|---|---|---|
| Flatness | Yes | No |
| Parallelism | Yes | Yes |
| Perpendicularity | Yes | Yes |
Two-Datum References
Orientation controls can reference multiple datums for complete constraint:
FCF: ┌───┬──────┬────────┬────────┐
│ ⊥ │ 0.1 │ A │ B │
└───┴──────┴────────┴────────┘This means: perpendicular to datum A AND parallel to datum B.
Composite Tolerance Zones
Surface Zone
For surfaces, the tolerance zone is two parallel planes:
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- Width equals the tolerance value
- Orientation locked to datum(s)
Axis Zone
For features of size, the tolerance zone is a cylinder:
- Diameter equals the tolerance value
- Axis orientation locked to datum(s)
Quick Reference Table
| Control | Symbol | Angle to Datum | Zone Shape | Typical Use |
|---|---|---|---|---|
| Parallelism | ∥ | 0° (parallel) | 2 planes or cylinder | Sliding surfaces |
| Perpendicularity | ⊥ | 90° | 2 planes or cylinder | Mounting holes |
| Angularity | ∠ | Any angle | 2 planes or cylinder | Chamfers, tapers |
Key Takeaways
- Orientation controls ALWAYS reference datums
- Parallelism: feature parallel (0°) to datum
- Perpendicularity: feature at 90° to datum
- Angularity: feature at any specified angle
- Orientation controls also control form (but not location)
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Next Lesson: Location Controls - controlling where features are positioned.
